The present invention relates to a method for making panels, to the apparatus for providing this method and to the panels obtained thereby.
The panels whereto the present invention relates consist of essentially stratified flat structures with uniform thickness. These can be successively heat-molded after the step which provides their formation and can be used, indeed as panels, to form finished items such as, for example, internal coverings of automotive vehicles.
The starting material for the preparation of these panels substantially consists of a thermoplastic resin and an organic filler. Conventional methods and the related devices for producing these panels entail a separate mixing step, wherein a certain amount of a thermoplastic resin is placed in close contact with the organic filler. The latter substantially consists of wood powder or sawdust, desiccated in a step previous to the mixing step, stored and then transferred to the subsequent processing steps (with problems of protecting the desiccated product from external humidity). In known methods and devices of the type at issue, the particles or fragments of organic filler must be sifted and selected, since they must have (due to processing requirements) controlled and uniform dimensions. Furthermore, they must be added to the mix in amounts not exceeding 60% by weight, while it would be preferable to use greater amounts of this less expensive component. The aforementioned mixture is traditionally prepared in a turbo-mixer and the mixture thus obtained is subsequently transferred to a plastication and extrusion unit, provided separately from the previous units, and whereto corresponds a separate step of conventional methods. The material thus extruded is subsequently laminated. In traditional devices, lamination is performed in a device with rollers or cylinders which subjects the layer of material in output from the extruder to a traction force. This force can in turn lead to discontinuities and irregularities on the surface of the finished panel, or even lacerate the layer of extruded material. The panel laminated with known devices is furthermore "uncovered", that is, it does not have the coatings and reinforcements which may instead be required for particular final applications of the panels. The transfer of the desiccated organic filler to the mixing step and the transfer of the mixture to the plastication and extrusion unit is a problem of known devices and methods, as well as for the above described reasons, also due to the fact that they make the overall process longer and more troublesome, and increase the complexity of the apparatus by means of which this method is carried out.